Flex spline for meshing type gear device, and meshing type gear device having flex spline

ABSTRACT

A flex spline  1  used for a meshing type gear device includes an attachment portion  1   a , a thin-thickness tubular portion  1   b  continuing to the attachment portion and capable of being elastically deformed, and external teeth  1   c  formed at the tip end portion of the tubular portion away from the attachment portion. The thin-thickness tubular portion  1   b  is formed in a conical shape with an opening angle θ which is tapered in a direction from the attachment portion  1   a  toward the external teeth  1   c  before inserting a wave generator  3.

BACKGROUND OF THE INVENTION

The present invention relates to a flex spline used for a meshing typegear device (wave motion gear device) and the meshing type gear device(wave motion gear device) having the flex spline.

The meshing type gear device (wave motion gear device) is conventionallywell known which includes a flex spline having an attachment portionformed normally as a boss portion and coupled to an output extractionmember, a tubular portion with a thin thickness normally continuing tothe attachment portion through a diaphragm and capable of beingelastically deformed, and external teeth formed at the tip end portionof the tubular portion away from the attachment portion side; a circularspline having inner teeth which mesh with the external teeth of the flexspline and having the number of teeth slightly larger than that of theexternal teeth; and a wave generator which is formed in an ellipticalshape and engages with the inner side of the tubular portion of the flexspline thereby to flexibly deform the flex spline. In particular, themeshing type gear device called Harmonic Drive (trade name) is wellknown.

At the time of processing the inner cylinder of the flex spline 1,normally, both the teeth portion 1 c of the flex spline 1 and theattachment portion (boss portion) 1 a thereof on the opposite side aregrasped by a chuck of a lathe etc., and a bite and the flex spline arerelatively moved in the shaft line direction while both the toothportion and the attachment portion are rotated around the shaft linesthereof thereby to perform the cutting process thereof.

To this end, in the conventional flex spline 1, as shown in FIG. 4A, thetubular portion 1 b with a thin thickness is formed in a straightcylindrical shape. That is, as shown in FIG. 4A, the inner diameter d1on the attachment portion (boss portion) 1 a side is equal to the innerdiameter d2 on the thin-thickness tubular portion 1 b side, that is,d1=d2. Each of the inner diameter d1 and the inner diameter d2 is set tobe smaller than the pitch diameter d0 of the inner teeth 5 a of acircular spline 5 described later.

In such a conventional meshing type gear device (wave motion geardevice), usually, the attachment portion (boss portion) 1 a isconfigured to be hardly deformed in order to fix the flex spline 1 andextracting an output torque. On the other hand, in the conventionalmeshing type gear device, as shown in Japanese Patent Laid-Open No.17888/1994 and Japanese Utility Model Laid-Open No. 173851/1986, theteeth portion 1 c of the flex spline 1 is formed on the thin-thicknesstubular portion 1 b and the teeth portion 1 c on the outer side of theflex spline 1 can be meshed with the teeth portion 5 a of the circularspline 5.

The wave generator 3 having a cam formed in an elliptical shape isinserted-through a bearing 4 into the inner diameter portion at the tipend of the tubular portion 1 b of the flex spline 1. The tooth portion 1c on the outer side of the flex spline 1 meshes with the circular spline5 in a manner that the flex spline 1 is deformed by the wave generator3, and the radius position of the tooth portion 1 c of the flex spline 1at which the major axis of the ellipse of the wave generator 3 ispositioned is made positioned on the outer side from the radius positionbefore the deformation.

As described above, the tubular portion 1 b of the flex spline 1 isformed in the straight cylindrical shape. Thus, in the flex spline 1where the wave generator 3 is inserted into the inner diameter portionof the tubular portion, the attachment portion 1 a does not deform. Incontrast, since the teeth portion 1 c of the thin-thickness tubularportion 1 b is expanded outwardly as shown in FIG. 4B by means of thewave generator 3, the tooth trace of the flex spline 1 having beendeformed does not become in parallel to the tooth trace of the circularspline 5, so that a coning angle α is formed at the teeth portion.

Thus, the meshing depth between the external teeth 1 c of the flexspline 1 and the inner teeth 5 a of the circular spline 5 differs in thetooth-width direction (that is, the shaft line direction of the flexspline 1). Since the meshing depth differs in the tooth-width direction,the load is not applied uniformly over the entire width of the tooth butapplied to a portion of the tooth concentrically. Usually, although eachof the external teeth 1 c of the flex spline 1 and the inner teeth 5 aof the circular spline 5 is a spur tooth, a normal meshing state can notbe obtained between these spur external teeth 1 c and 5 a.

Further, due to the influence of the aforesaid coning angle α of theflex spline 1, the wave generator 3 is made in contact only on its oneend side with the inner diameter portion of the flex spline 1 whenviewed along the shaft line direction of the flex spline 1. Thus, thelife time of the bearing 4 attached between the wave generator 3 and theflex spline 1 is reduced and the meshing rigidity between the wavegenerator 3 and the flex spline 1 is also degraded.

Furthermore, even if a roller bearing with a large bearing capacity istried to be attached between the wave generator 3 and the flex spline 1,due to the aforesaid coning angle α and the one end side contact stateof the wave generator caused by the coning angle, the roller of theroller bearing inclines and so the inner wheel and the outer wheel ofthe bearing are abraded or worn out by the shoulder portion of theroller. Thus, such a rolling bearing can be not be applied.

The shorter the length (the length along the axial direction) of thebody portion of the flex spline 1 becomes, the more the aforesaidvarious problems accompanied by the conventional technique becomeremarkable.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to eliminate the problemsaccompanied by the conventional technique and to provide a flex splinefor a meshing type gear device (wave motion gear device) in which theconing angle α formed between the flex spline 1 and the circular spline5 is eliminated or reduced thereby to make the meshing depth between theexternal teeth 1 c of the flex spline 1 and the inner teeth 5 a of thecircular spline 5 uniform in the tooth-width direction, whereby a loadis uniformly applied over the entire width of the tooth and so a normalmeshing state is obtained thereby to improve torque transmissionaccuracy, torsional rigidity and load ability.

Further, an object of the invention is to provide a meshing type geardevice (wave motion gear device) having such a flex spline 1.

The aforesaid object is attained by a flex spline used for a meshingtype gear device which includes an attachment portion, a thin-thicknesstubular portion continuing to the attachment portion and capable ofbeing elastically deformed, and external teeth formed at a tip endportion of the tubular portion away from the attachment portion side,wherein the flex spline used for a meshing type gear device ischaracterized in that the thin-thickness tubular portion is formed in aconical shape which is tapered from the attachment portion side towardthe external teeth side.

That is, according to the invention, a maximum coning angle α which willbe caused when the wave generator is inserted is analyzed by taking therigidity and deformation of the entirety of the flex spline. Then, aconical shape having a tapered angle slightly smaller than the coningangle in the opposite direction of the coning angle is employed as theconfiguration of the flex spline in a free state. Thus, the coning angleα at the teeth of the flex spline is canceled by the tapered anglethereby to eliminate or reduce the coning angle between the flex splineand the circular spline in the meshed state.

In this case, the thin-thickness tubular portion of the flex splineaccording to the invention may be formed in the conical shape which istapered uniformly toward the external teeth side from the attachmentportion side. Alternatively, the tubular portion of the flex spline ofthe invention may be formed in a cylindrical shape over a predeterminedlength in the shaft line direction on the attachment portion side, andformed in a conical shape at the external teeth side portion continuingfrom the cylindrical portion so as to be tapered toward the externalteeth side.

The attachment portion of the invention is in many cases coupled to anoutput extracting member. Thus, when the flex spline is configured in acap shape, the attachment portion may be a projection portion formed asa boss portion at the bottom portion (diaphragm) of the cap. In somecase, the flex spline is configured in a tubular shape having no bottomportion. In this case, the attachment portion may be formed as a ringportion on the opposite side of the tooth portion of the tubularportion.

Further, the invention provides a meshed type gear device having such aflex spline. That is, the meshing type gear device includes a flexspline having an attachment portion, a thin-thickness tubular portioncontinuing to the attachment portion and capable of being elasticallydeformed, and external teeth formed at a tip end portion of the tubularportion away from the attachment portion side; a circular spline havinginner teeth to be meshed with the external teeth of the flex spline; anda wave generator elastically deforming the flex spline, wherein themeshing type gear device is characterized in that the thin-thicknesstubular portion is formed in a conical shape which is tapered from theattachment portion side toward the external teeth side, and the wavegenerator is provided with a plural lines of bearings abutting againstan inner periphery of the flex spline. Alternatively, the thin-thicknesstubular portion is formed in a conical shape which is tapered from theattachment portion side toward the external teeth side, and the wavegenerator is provided with a roller bearing abutting against an innerperiphery of the flex spline.

In these cases, also the thin-thickness tubular portion of the flexspline may be formed in the conical shape which is tapered uniformlytoward the external teeth side from the attachment portion side.Alternatively, the tubular portion of the flex spline may be formed in acylindrical shape on the attachment portion side, and formed in aconical shape at the external teeth side portion continuing from thecylindrical portion so as to be tapered toward the external teeth side

The present disclosure relates to the subject matter contained inJapanese patent application No. P2001-376965 (filed on Dec. 11, 2001),which is expressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are diagrams showing a first embodiment of the invention,in which FIG. 1A shows a sectional diagram of a cap-shaped flex splinewhich is tapered toward the tip end thereof, FIG. 1B shows a sectionalview of one embodiment of a meshing type gear device (wave motion geardevice) having a flex spline shown in FIG. 1A, and FIG. 1C shows asectional view of another embodiment of a meshing type gear device (wavemotion gear device) having a flex spline shown in FIG. 1A.

FIGS. 2A to 2C are diagrams showing a second embodiment of theinvention, in which FIG. 2A shows a sectional diagram of a cap-shapedflex spline which is formed in a cylindrical shape over a predeterminedlength in the shaft line direction at an attachment portion side and isformed at an external teeth side portion continuing from the cylindricalwhich is tapered toward the external teeth thereof, FIG. 2B shows asectional view of one embodiment of a meshing type gear device (wavemotion gear device) having a flex spline shown in FIG. 2A, and FIG. 2Cshows a sectional view of another embodiment of a meshing type geardevice (wave motion gear device) having a flex spline shown in FIG. 2A.

FIGS. 3A and 3B are diagrams showing another embodiment of theinvention, in which FIG. 3A shows a sectional diagram of a flex splineformed in a cylindrical shape having no bottom portion and formed in aconical shape being tapered toward the tip end, and FIG. 3B shows asectional view of a meshing type gear device (wave motion gear device)having a flex spline shown in FIG. 3A.

FIGS. 4A and 4B are diagrams showing an example of a conventionaldevice, in which FIG. 4A shows a sectional diagram of a flex spline andFIG. 4B shows a sectional view of a meshing type gear device (wavemotion gear device) having a flex spline shown in FIG. 4A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiments of the invention will be explained in detail withreference to the accompanying drawings. FIG. 1A shows a sectional viewof the first embodiment of a flex spline 1 according to the invention.

The flex spline 1 is formed by special steel with high fatigue strength.The flex spline 1 according to the embodiment shown in FIG. 1A isconfigured in a cap shape with a bottom portion, and a boss portionprotruding from the bottom portion (diaphragm) 1 d of the cap serves asan attachment portion 1 a of the invention.

A tubular portion 1 b with a thin thickness is continued to theattachment portion 1 a through the bottom portion (diaphragm) 1 d andexternal teeth 1 c is formed at the outside of the tip end of thetubular portion 1 b. In this embodiment, the tubular portion 1 b isformed in a conical shape which is tapered uniformly toward the externalteeth 1 c side from the attachment portion 1 a side.

That is, as shown in FIG. 1A, the inner diameter D1 on the attachmentportion (boss portion) 1 a side of the tubular portion is 1 b of theflex spline 1 is larger than the inner diameter D2 on the tip end sidethereof, that is, D1>D2.

Before inserting a wave generator 3, the flex spline 1 is formed in aconical shape with an angle θ by taking an assumed opening angle of theflex spline at the time of inserting the major axis of the wavegenerator 3 into consideration. This angle θ formed in advance ispreferably an intermediate value of the opening angle as represented bythe following expression.θ=[tan⁻¹{(δ/2)/L}]/2In this expression, δ/2 is a half (one side) of a deviation value δ atthe major axis portion at the time of inserting the wave generator 3,and L is the length of the body portion of the flex spline. The angle θcan be set freely in a range of about 0.5 to 5 degrees.

Before inserting the wave generator 3, the inner diameter D1 on theattachment portion (boss portion) 1 a side of the tubular portion 1 b ofthe flex spline 1 may be set to be larger than or equal to the innerdiameter d1 on the attachment portion (boss portion) 1 a side of theconventional flex spline. In the latter case, the pitch circle of theexternal teeth 1 c of the flex spline 1 is made larger. Further, beforeinserting the wave generator 3, the inner diameter D1 on the attachmentportion (boss portion) 1 a side of the tubular portion 1 b of the flexspline 1 is smaller than the diameter of the pitch circle of the innerteeth 5 a of the circular spline 5.

FIG. 1B shows a sectional view of the meshing type gear device (wavemotion gear device) having the flex spline 1 shown in FIG. 1A.

The circular spline 5 formed in an annulus ring shape is fixedlyprovided on the outside of the tip end of the tubular portion 1 b of theflex spline 1 such that the inner teeth 5 a formed on the innerperiphery of the circular spline 5 can mesh with the external teeth 1 cof the flex spline 1. The number of teeth of the inner teeth 5 a formedat the circular spline 5 is slightly larger than that of the externalteeth 1 c of the flex spline 1 (larger by 2 in the embodiment).

The wave generator 3 is provided so as to be rotatable on the inner sideof the tip end of the tubular portion 1 b of the flex spline 1.Normally, input is transmitted to the wave generator 3. The wavegenerator 3 is formed in an elliptical shape and has a cam. The innerring of the bearing 4 is attached to the outer periphery of the cam ofthe wave generator 3 formed in the elliptical shape and the outer ringof the bearing 4 can engage with the inner side of the tubular portionof the flex spline 1.

When the wave generator 3 is inserted, the inner teeth 5 a of thecircular spline 5 mesh with the external teeth 1 c of the flex spline 1in a certain range, at the major axis portion. However, it is preferablethat the pitch circle at the average meshing position is set to coincidewith the pitch circle of the circular spline 5.

As described above, the wave generator 3 is configured by the cam formedin the elliptical shape and the bearing 4 which inner ring is attachedto the cam and which outer ring engages with the inside of the tubularportion 1 b of the flex spline 1. When input is transmitted to the wavegenerator 3, the wave generator flexibly deforms the flex spline 1through the bearing 4. Further, as described above, the circular spline5 has the inner teeth 5 a meshing with the external teeth 1 c of theflex spline 1, and the number of teeth of the inner teeth 5 a is set tobe slightly larger than that of the external teeth 1 c of the flexspline (usually larger by 2).

When input is transmitted to the wave generator 3, the flex spline 1 isdeflected in an elliptical shape by the wave generator 3, whereby theexternal teeth 1 c of the major axis portion of the flex spline 1 thusdeflected in the elliptical shape mesh with the inner teeth 5 a of thecircular spline 5 and the external teeth 1 c of the minor axis portioncompletely separate from the inner teeth 5 a of the circular spline.Since the circular spline 5 is fixed in the aforesaid manner, when thewave generator 3 is rotated in one direction (for example, clockwise),the flex spline 1 deforms elastically and the meshing position betweenthe external teeth 1 c of the flex spline 1 and the inner teeth 5 a ofthe circular spline 5 moves sequentially. When the wave generator 3rotates by 180 degrees clockwise, the flex spline 1 movescounterclockwise by a distance corresponding to one tooth. In thismanner, when the wave generator 3 rotates by one revolution (360degrees) clockwise, the flex spline 1 moves counterclockwise by adistance corresponding to two teeth since the flex spline 1 is smallerin its number of the teeth by two than that of the circular spline 5. Inthis manner, the input transmitted to the wave generator 3 is reduced inits speed to a large extent and taken out from the flex spline 1.

As described above, since the tubular portion 1 b of the conventionalflex spline 1 is formed in the straight cylindrical shape, the coningangle α is formed. Thus, the meshing depth between the external teeth 1c of the flex spline 1 and the inner teeth 5 a of the circular spline 5differs in the tooth-width direction (that is, the shaft line directionof the flex spline 1). Since the meshing depth differs in thetooth-width direction in this manner, the load is not applied uniformlyover the entire width of the tooth but applied to a portion of the toothconcentrically. Thus, there arise a problem that although each of theexternal teeth 1 c of the flex spline 1 and the inner teeth 5 a of thecircular spline 5 is a spur tooth usually, a normal meshing state cannot be obtained between these spur external teeth 1 c and 5 a.

In order to solve such a problem accompanied by the conventionaltechnique, according to the invention, a maximum coning angle α whichwill be caused when the wave generator 3 is inserted is analyzed bytaking the rigidity and deformation of the entirety of the flex spline1. Then, as shown in FIG. 1A, a conical shape having a tapered angle θalmost same as the aforesaid coning angle α in the opposite direction ofthe coning angle α is employed as the configuration of the flex spline 1in a free state. Thus, the coning angle α at the teeth of the flexspline is canceled by the tapered angle θ thereby to eliminate or reducethe coning angle α between the flex spline 1 and the circular spline 5in the meshed state.

According to the invention, the coning angle α formed between the flexspline 1 and the circular spline 5 is eliminated or reduced. Thus, asshown in FIG. 1B, the meshing depth between the tooth 1 c of the flexspline 1 and the tooth 5 a of the circular spline 5 becomes uniform inthe tooth-width direction. As a result, a load is applied uniformly overthe entire width of each of the teeth of the flex spline and thecircular spline, so that a normal meshing state can be obtained andhence the meshing type gear device (wave motion gear device) can beprovided in which torque transmission accuracy, torsional rigidity andload ability is improved.

Further, according to the invention, since the tooth 1 c of the flexspline 1 meshes with the tooth 5 a of the circular spline 5 with theuniform meshing depth in the tooth-width direction, a plural lines ofthe bearings 4, 4 (two lines in the illustrated embodiment) abuttingagainst the inner periphery of the flex spline 1 can be attached to theouter periphery of the cam of the wave generator 3, as shown in FIG. 1C.In such a case, a load can also be applied uniformly to each of thebearings 4, 4 and so a normal meshing state can be obtained.

FIG. 2A shows a sectional view of a flex spline 1 according to thesecond embodiment of the invention. The thin-thickness tubular portion 1b of the flex spline 1 according to the first embodiment is formed inthe conical shape which is tapered uniformly toward the external teeth 1c side from the attachment portion 1 a side. Alternatively, the flexspline 1 of the second embodiment shown in FIG. 2A is formed in acylindrical shape (inner diameter is D1) over a predetermined length 1in the shaft line direction on an attachment portion 1 a side, andformed in a conical shape at the external teeth side portion 1 bcontinuing from the cylindrical portion so as to be tapered toward theexternal teeth side (inner diameter of the tip end portion is D2). Thesize of the flex spline 1 according to this embodiment is set like theaforesaid embodiment. In this embodiment, the length L of the bodyportion of the flex spline 1 is the length of a portion formed in theconical shape. Thus, in this embodiment, the angle θ formed in advanceis slightly larger than that of the aforesaid embodiment.

In the same manner as FIG. 1B, the meshing type gear device (wave motiongear device) having the flex spline 1 of the second embodiment can beobtained by using the flex spline 1 of the second embodiment shown inFIG. 2A (see FIG. 2B). The input transmitted to the wave generator 3 isreduced in its speed to a large extent and taken out from the flexspline 1.

Like the aforesaid embodiment, according to this embodiment, the coningangle α formed between the flex spline 1 and the circular spline 5 iseliminated or reduced. Thus, as shown in FIG. 2B, the meshing depthbetween the tooth 1 c of the flex spline 1 and the tooth 5 a of thecircular spline 5 becomes uniform in the tooth-width direction. As aresult, a load is applied uniformly over the entire width of each of theteeth of the flex spline and the circular spline, so that a normalmeshing state can be obtained and hence the meshing type gear device(wave motion gear device) can be provided in which torque transmissionaccuracy, torsional rigidity and load ability is improved.

Further, according to the invention, the tooth 1 c of the flex spline 1meshes with the tooth 5 a of the circular spline 5 with the uniformmeshing depth in the tooth-width direction. Thus, like the embodimentshown in FIG. 1C, a plural lines of the bearings 4 (two lines in theillustrated embodiment) abutting against the inner periphery of the flexspline 1 may be attached to the outer periphery of the cam of the wavegenerator 3 so that a load is applied uniformly to each of the bearingsthereby to obtain a normal meshing state.

Further, as shown in FIG. 2C, a roller bearing 4′ abutting against theinner periphery of the flex spline 1 may be attached to the outerperiphery of the cam of the wave generator 3 in place of the plurallines of the bearings 4, 4. The meshing depth between the tooth 1 c ofthe flex spline 1 and the tooth 5 a of the circular spline 5 becomesuniform in the tooth-width direction. As a result, a load is applieduniformly over the entire width of each of the teeth of the flex splineand the circular spline, so that a normal meshing state can be obtained.Thus, even in the case of employing the roller bearing 4′, none of theinner wheel or the outer wheel of the bearing are abraded or worn out bythe shoulder portion of the roller of the roller bearing 4′ and hencethe meshing type gear device (wave motion gear device) can be providedin which torque transmission accuracy, torsional rigidity and loadability is improved.

In the aforesaid embodiment shown in FIG. 1C, the roller bearing 4′ mayalso be used in place of the plural lines of the bearings 4, 4.

In the aforesaid first and second embodiments, the flex spline 1 isformed in the cap shape and the attachment portion 1 a is the projectionportion formed as the boss portion at the bottom portion of the cap.Alternatively, the invention can be applied to a case where the flexspline 1 is formed in a cylindrical shape having no bottom portion. Inthis case, as shown in FIGS. 3A and 3B, the attachment portion 1 a isformed as an annular ring portion at the outer periphery of the endportion on the opposite side of the tooth portion 1 c of the tubularportion 1 b. FIG. 3A is a sectional view of the flex spline 1 of acylindrical shape having no bottom portion formed in a conical shapewhich is tapered uniformly toward an external teeth side. FIG. 3B is asectional view of the meshing type gear device (wave motion gear device)having the flex spline 1 shown in FIG. 3A.

As described above, according to the invention, the problem accompaniedby the aforesaid conventional technique is eliminated. That is, theconing angle α formed between the flex spline 1 and the circular spline5 is eliminated or reduced. Thus, the meshing depth between the tooth 1c of the flex spline 1 and the tooth 5 a of the circular spline 5becomes uniform in the tooth-width direction. As a result, a load can beapplied uniformly over the entire width of each of the teeth of the flexspline and the circular spline, so that a normal meshing state can beobtained and hence the flex spline 1 for the meshing type gear device(wave motion gear device) can be provided in which torque transmissionaccuracy, torsional rigidity and load ability is improved.

Further, according to the invention, the meshing type gear device (wavemotion gear device) having such the flex spline 1 can be provided.

1. A flex spline used for a meshing type gear device, comprising: anattachment portion; a thin-thickness tubular portion continuing to theattachment portion and capable of being elastically deformed; andexternal teeth formed at a tip end portion of the tubular portion awayfrom the attachment portion, wherein the thin-thickness tubular portionis formed at least partly in a conical shape which is tapered in adirection from the attachment portion toward the external teeth when ina relaxed, undeformed state.
 2. A flex spline used for a meshing typegear device according to claim 1, wherein the thin-thickness tubularportion has an attachment portion side part in a straight cylindricalshape, and an external teeth side part in the conical shape, whichcontinues from the cylindrical attachment portion side part.
 3. Ameshing type gear device comprising: a flex spline having an attachmentportion, a thin-thickness tubular portion continuing to the attachmentportion and capable of being elastically deformed, and external teethformed at a tip end portion of the tubular portion away from theattachment portion; a circular spline having inner teeth to be meshedwith the external teeth of the flex spline; and a wave generatorelastically deforming the flex spline, wherein the thin-thicknesstubular portion is formed at least partly in a conical shape which istapered in a direction from the attachment portion toward the externalteeth when in a relaxed, undeformed state, and wherein the wavegenerator has plural lines of bearings abutting against an innerperiphery of the flex spline.
 4. The meshing type gear device of claim 3wherein an attachment portion side of the thin-thickness tubular portionhas an inner diameter that is greater than or equal to a maximum meshinglength of the wave generator, and a tip end portion side of thethin-thickness tubular portion has an inner diameter that is less thanthe maximum meshing length of the wave generator.
 5. The meshing typegear device of claim 3 wherein the wave generator has a maximum meshinglength substantially equal to an inner diameter of an attachment portionside of the thin-thickness tubular portion of the flex spline.
 6. Themeshing type gear device of claim 3 wherein the wave generator has amaximum meshing length less than or equal to an inner diameter of anattachment portion side of the thin-thickness tubular portion of theflex spline.
 7. A meshing type gear device comprising: a flex splinehaving an attachment portion, a thin-thickness tubular portioncontinuing to the attachment portion and capable of being elasticallydeformed, and external teeth formed at a tip end portion of the tubularportion away from the attachment portion; a circular spline having innerteeth to be meshed with the external teeth of the flex spline; and awave generator elastically deforming the flex spline, wherein thethin-thickness tubular portion is formed at least partly in a conicalshape which is tapered in a direction from the attachment portion towardthe external teeth when in a relaxed, undeformed state, and wherein thewave generator has a roller bearing abutting against an inner peripheryof the flex spline.
 8. The meshing type gear device of claim 7 whereinthe wave generator has a maximum meshing length substantially equal toan inner diameter of an attachment portion side of the thin-thicknesstubular portion of the flex spline.
 9. The meshing type gear device ofclaim 7 wherein the wave generator has a maximum meshing length lessthan or equal to an inner diameter of an attachment portion side of thethin-thickness tubular portion of the flex spline.
 10. The meshing typegear device of claim 7 wherein an attachment portion side of thethin-thickness tubular portion has an inner diameter that is greaterthan or equal to a maximum meshing length of the wave generator, and atip end portion side of the thin-thickness tubular portion has an innerdiameter that is less than the maximum meshing length of the wavegenerator.